From Halopedia, the Halo wiki
The artifact is a squat cylinder that is roughly the size of a tire or suitcase. It has Braille-like triangles, lines, and dots set in the metal in an ordered, non-repeating pattern running around the rim like a tire tread. On the top center is a raised square approximately the size of a human palm. Some of the artifact is made of osmium while the rest of the material was unidentifiable by the crew of Apocalypso but it is known to be denser than Osmium.
Prior to its activation, it was letting off very faint, but complex, magnetic fields. After its activation, it let out one massive electromagnetic pulse that was strong enough to temporarily knock out all the communications equipment within the Solar System for seven seconds before changing into a series of oscillating pulses that grew steadily weaker.
The object is activated by touching all the triangles, then all the lines, and then the dots, in that particular sequence. Its deactivation sequence is the exact opposite: dots, lines, triangles.
After a brief study of the artifact, Captain Greene feared that the Covenant had done something to their artificial intelligence construct, Melissa, and the ship headed back to Earth. Melissa was indeed affected by a hostile Covenant AI called the Seeker which desired any and all Forerunner-related data. The foreign AI used Melissa to influence a crew member named MacKaskill to fiddle with the artifact. When they exited Slipspace, the artifact let out an enormous electromagnetic pulse that neutralized all communications in the Solar system for seven seconds, caused the ship to crash in Lunar orbit, and fragmented Melissa. One piece of the AI landed in Jersey Morelli's home computer, and the other was also thrown back in time to the year 2004.
The artifact was taken to Chawla Base in Boston, Massachusetts for study. An ambitious Major Standish believed it to be Covenant technology and decided to take the glory and had the surviving crew hunted down and killed. This was noticed by one of Melissa's fragments, now named Durga, who was looking in on the Apocalypso's destruction. Durga led a vigilante group that broke into Chawla Base and turned off the artifact, using information acquired by her other fragment. The artifact let out another massive pulse, which closed the temporal anomaly and reunited the fragments.
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